A complainant contacted Ofcom about an episode of American Dad! - the show created by Seth MacFarlane following a dysfunctional American family headed by CIA agent Stan Smith - which aired on FX on August 11 at 8.30pm.

The episode in question featured a storyline revolving around Stan bullying his son, Steve, in order to make him stand up for himself.

It included a flashback scene shown at 8.48pm in which Francine, Stan's wife, recalled stabbing and killing someone when she was a teenager. The sequence lasted 13 seconds and showed Francine fighting another girl in an underground fight club.

The other woman produced a knife and stabbed Francine in the shoulder, but then Francine retrieved the knife and stabbed the woman in the stomach, killing her. Ofcom observed that she "then triumphantly taunted the dead girl".

In the same episode, there was also a prolonged 90-second sequence involving Stan repeatedly being kicked and punched by a man who had bullied him as a child.

Ofcom further noted three occasions of Stan making sexual taunts, such as stealing Steve's bike and then saying: "I'm gonna mount this and ride it hard. Like I did your mom last night."

Fox said that it takes violence "very seriously" and accepted that the episode of American Dad! should not have been shown before the 9pm TV watershed.

It said that this was down to "human error", as the '15' rating given to the episode, meaning it should not be shown before 9pm, was not picked up by its compliance teams.

Fox International said that it was moving to a new automatic checking system which "will prevent programs being scheduled in unsuitable slots", and in the meantime it is manually reviewing all episodes of American Dad! to prevent further slip-ups.

In its latest Broadcast Bulletin, Ofcom said that the scenes of violence and sexual taunts in the American Dad! episode were "unsuitable for children".

The regulator said that considering the content and the fact that the program was aired on a Saturday evening, when children were more likely to be watching, young viewers were not sufficiently protected by Fox from the "unsuitable material".

"Ofcom had concerns about the compliance procedures in place because material suitable for a post-watershed transmission only was scheduled for broadcast pre-watershed, even though [Fox] had already reviewed it previously and decided it should only be shown after 9pm," Ofcom said.

"Compliance with the Code therefore relied on manual checks picking up inappropriate scheduling and - as in this case - such a compliance arrangement was clearly not satisfactory.

"Ofcom expects Fox International to complete its review of its compliance arrangements for scheduling and put in place revised and robust arrangements as soon as possible."